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%I #4 Sep 03 2015 07:01:25
%S 1,7,28,476,1386,8106,117936,322764,1440579,6172495,99773646,
%T 232110704,981073576,3329628176,14040114012,224848217580,490210909629,
%U 1828885568055,5750093241172,20040621544916,69910543160794,1238596672832718,2451410591056280,8705347941656016
%N Number of compositions of n into distinct parts where each part i is marked with a word of length i over a septenary alphabet whose letters appear in alphabetical order.
%C Also matrices with seven rows of nonnegative integers with distinct positive column sums and total element sum n.
%H Alois P. Heinz, <a href="/A261845/b261845.txt">Table of n, a(n) for n = 0..5000</a>
%p b:= proc(n, i, p) option remember;
%p `if`(i*(i+1)/2<n, 0, `if`(n=0, p!, b(n, i-1, p)+
%p `if`(i>n, 0, b(n-i, i-1, p+1)*binomial(i+6, 6))))
%p end:
%p a:= n-> b(n$2, 0):
%p seq(a(n), n=0..25);
%Y Column k=7 of A261835.
%K nonn
%O 0,2
%A _Alois P. Heinz_, Sep 03 2015
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